Mediocactus hahnianus: A resolved enigma and a new chapter of its history

Abstract

The first discovery of Mediocactus hahnianus was attributed to Harry Blossfeld. Based on literature analysis, it is shown that T. Rojas and A.M. Friedrich plausibly made the discovery in the mid-1930s, and that seeds or cuttings were then given to Marsoner and eventually arrived at R. Blossfeld's nursery via H. Blossfeld. Although cultivated in Europe by Hahn, the plant is presently known only from the clone grown by J. West in the US, and obtained from Rojas in 1937. Recently, a new colony has been found and it seems to be a single clone. It perfectly fits the US clone from the point of view of morphology, flowers, growth habit, chromosome number, and seed morphology, whereas the localities are 400 km away from each other. Taxonomy and nomenclature are discussed: We decided to retain the species in Trichocereus, using a conservative concept for the genus based on morphological characters. A neotype for Mediocactus hahnianus is designated here.